Portable desk



FIG. 1 is a top plan view of a portable desk showing our new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a left side elevational view;

FIG. 5 is a right side elevational view; and,

FIG. 6 is a bottom plan view thereof. 

The ornamental design for a portable desk, as shown and described. 